Assessing tungsten-based electrodes coated with W and Ce oxides for pH sensing applications

Abstract

This study assessed tungsten-based materials with and without dispersed CeO2 for potential use as pH sensors. Specifically, three types of tungsten electrodes were characterized: tungsten electrodes without CeO2 but with native oxide, tungsten electrodes without CeO2 that were oxidized, and a tungsten electrode containing dispersed CeO2 that was oxidized, resulting in a mixture of WO3, CeO2, and Ce2O3. The characterization was performed using SEM/EDAX, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The oxide coatings showed higher oxygen contents compared to native tungsten. XPS confirmed the presence of a thick layer of WO3 and cerium oxides. The electrodes exhibited good reproducibility and stability in pH measurements. A linear relationship was found between the open circuit potential and pH, with slopes of 44.9, 40.8, and 46.9 mV pH−1 for native oxide, WO3, and WO3 with CeO2 and Ce2O3, respectively. The latter showed the highest sensitivity and lowest hysteresis. The response times ranged from 14.5–23.5 s and were faster in acidic solutions. Overall, the inexpensive tungsten-based electrodes demonstrated promising capabilities for pH sensing, but in particular ceriated tungsten electrodes.